Characterization of diamond-like carbon films before and after heavy energetic ion implantations

Abstract

Hydrogenated diamond-like carbon films were implanted by 110 keV Fe + at doses ranging from 1 × 10 13 to 5 × 10 16 ions cm −2. The film resistivities and the infra-red transmittances of the specimens were determined as functions of the implanted doses. Raman spectra and the infra-red transmittances of the film layers were used to characterize the structural changes of the implanted films. It was found that, when the implantation dose was higher than about 5 × 10 14 or 1 × 10 15 ions cm −2, the film resistivity and the total infra-red transmittance of the specimens decreased significantly. However, when the dose was smaller than this value, the resistivity decreased firstly and then increased with dose and the measured values were higher than those of corresponding as-grown ones. The infra-red transmittance of the specimens was also improved to some extent under the lower dose range. By using structural characterization results, especially the infra-red transmittances of the film layers, we conclude that the electrical and optical property changes at doses higher than about 5 × 10 14 or 1 × 10 15 ions cm −2 were due to the following changes, i.e., the decrease in the population of both sp 2 C-H and sp 3 C-H bonds (compared with that of sp 3 C-H bonds, the decrease in speed of sp 2 C-H bonds is smaller), the decrease of bond-angle disorder and the increased population of sp 2 C-C bonds. However, at doses between 1 × 10 14 and 5 × 10 14 or 1 × 10 15 ions cm −2, the implantation induced increase of C-H bonds was responsible for the observed property changes. Compared with the previous reports, the novelty of the present work is: the IR transmittance curves of the single film layers give us direct evidence for the changes of different C-H bonds with increasing ion dose and thus proved the transformation mechanism proposed previously.